1. Field of the Invention
The present invention relates to a nuclear fuel rod for a fast reactor, and more particularly, to a nuclear fuel rod for a fast reactor in which a reactor core of a sodium-cooled fast reactor (SFR) is designed compact-sized.
2. Description of the Related Art
The fast reactor is generally known for pyroprocessing in which nuclear waste from the light water reactor is recycled.
The fast reactor, and more specifically, the sodium-cooled fast reactor (SFR) continuously breeds more fuel for fission in the reactor than it consumes. Further, the nuclear waste from the light water reactors has relatively long half life and nucleus with high radiotoxicity is split into more stable nuclei with reduced radiotoxicity by the transmutation in SFR. With high utilization of the fuel, sustained energy supply can be provided while waste is reduced by SFR.
FIG. 5 illustrates a constitution of a conventional nuclear fuel rod for a fast reactor.
Referring to FIG. 5, the conventional nuclear fuel rod for the fast reactor includes a slender cylindrical fuel material 10, and a cladding tube 20 in a tubular form surrounding the material 10.
The fast reactor is designed to be cooled by liquid metal such as sodium (Na), lead (Pb), lead-bismuth (Pb—Bi) alloy instead of water which is used as a coolant in the light- or heavy-water reactor. It is also possible to cool the heat generated from the slug 10 by feeding liquid metal 30 also into the cladding tube 20.
Meanwhile, in the conventional nuclear fuel rod for the fast reactor, plenum, which is the space to collect fission products (specifically, fission gas), is placed above the materials, taking up approximately 42% of the entire length of the nuclear fuel rod.
The plenum is considered to be one of the important factors that influence inner pressure of the fuel rod due to release of fission products (specifically, fission gas) according to the consumption of the nuclear fuel. In determining the overall length of the nuclear fuel rod and determining height of the reactor core, it is necessary to reduce the overall length of the nuclear fuel rod by reducing the length of the plenum for the purpose of compacter reactor.
By way of example, Korean Patent Application No. 10-2007-0082795 (Korean Patent No. 1009156020000) (title: Fuel rod coated with oxide film on inner surface of the cladding and its manufacturing method) proposes a technology to extend the lifespan of the fast reactor by forming an oxide film on an inner surface of the cladding tube of the nuclear fuel rod for fast reactor, thereby suppressing fuel cladding chemical interaction (FCCI) between metallic fuel slug and cladding tube and increasing maximum allowable degree of burnup and maximum allowable temperature.
FIG. 6 illustrates another constitution of a conventional nuclear fuel rod for fast reactor.
Referring to FIG. 6, the nuclear fuel rod for fast reactor of Korean Patent No. 1009156020000 has a film of oxide selected from a group consisting of chromium oxide (Cr2O3), Vanadium oxide (V2O3) and zirconium oxide (ZrO2) which is coated on an inner surface of the cladding tube, in which the oxide film suppresses chemical reaction between the metallic slug and the cladding tube to thus increase temperature at the outlet of the fast reactor. However, the above-mentioned patent inherently has a problem of difficulty of designing compact-sized reactor core, due to the metallic slug that is structurally identical to the conventional fuel slug.
Korean Patent Application No. 10-2008-0011094 (Korean Patent No. 10-0959152) (title: Metallic fuel element with nitride-coated layer on cladding inner surface for fast nuclear reactor and manufacturing method thereof) discloses a technology to lift up the operational temperature limit by efficiently suppressing inter-diffusion reaction between metallic fuel slug received in the cladding tube and the cladding tube by stably forming nitride-coated layer of the transition elements on inner wall of the cladding tube, thereby preventing generation of inter-reaction layer between the metallic fuel slug and the inner wall of the cladding tube.
FIG. 7 illustrates a constitution of yet another conventional nuclear fuel rod for fast reactor.
Referring to FIG. 7, the metallic nuclear fuel for use in fast reactor includes a metallic fuel slug 1 of cylindrical configuration, a hollow cylindrical cladding tube 3 surrounding the metallic fuel slug 1, a nitride-coated layer 2 of transition element formed on inner wall of the cladding tube 3, and liquid metal 4 filled between the metallic fuel slug 1 and the cladding tube 3. While the conventional constitution aims to lift up the operational temperature limit by preventing generation of the inter-reacting layer between the metallic fuel slug 1 and the inner wall of the cladding tube 3 due to the nitride-coated layer 2, this still does not address the problem associated with the difficulty of forming compact-sized reactor core since the metallic fuel slug 1 is formed structurally identical to the conventional fuel slug.
Korean Pat No. 10-0963472 mentions metallic fuel rod including in the cladding tube a metal sheath having therein metallic fuel particles formed by atomizing technique, and a preparation method thereof. However, Korean Pat No. 10-0963472 does not describe about ensuring plenum space by defining a hollow space in the center occupied by the fuel material. That is, the patent only inserts metal sheath into cladding tube to prevent interaction between the fuel material and the cladding tube.
Accordingly, in order to solve the problems occurring in the prior art, the inventors have researched for a method for designing a compact-sized reactor core by structurally altering a nuclear fuel rod for a fast reactor and thus completed the present invention.